Two research programs are proposed: The first is a study of the psychophysiology of irritable bowel syndrome (IBS) whose long-term goal is to identify the physiological and psychological mechanisms for the symptoms of IBS (e.g., abdominal pain and alterations in bowel habits). Experiment compares patients who meet strict diagnostic criteria for IBS to patients with functional, bowel disorder (FBD), (abdominal pain plus altered bowel habits) with respect to colon EMG slow wave activity and contractile activity. Experiments 2 and 3 will investigate previously observed similarities in colon EMG activity between patients with IBS and patients with lactose malabsorption (LMA) by comparing LMA patients with borderline positive test results for lactose intolerance to LMA patients with definitive evidence of lactose intolerance. Dependent measures are small bowel transit time, colon EMG and contractile activity, small intestinal motility, and biopsy evidence for lactase enzyme deficiency. Experiment 4 investigates the contribution of air swallowing to IBS. Air swallowing, abdominal circumference, and volume of flatus are compared to self- ratings of abdominal pain and bloating in 15 IBS patients and 15 controls. The effects of injecting 500 ml of air into the duodenum on small intestinal and colonic motility and myoelectric activity will also be investigated. Experiment 5 tests whether excessive air swallowing can be suppressed via biofeedback. The second research program is a study of the determinants of illness behavior. Research questions are: (a) Does reinforcement of somatic complaints and modeling of the sick role by parents during adolescence predict increased numbers of somatic symptoms, disability days, and medical clinic visits in adults; and are these correlations independent of exposure to psychological stressors, psychometric measures of neuroticism, and physician ratings of biological dysfunction on physical examination? (b) Is there specificity of learning? Questionnaires will assess retrospectively the responses of parents to menstrual, cold, and bowel symptom in 35 non-pregnant clients of Planned Parenthood. These women will be given physical examinations by a gynecologist and those with bowel symptoms will be examined by a gastroenterologist to assess biological dysfunction. The Costa- McCrae Neuroticism Extroversion-Openness Inventory will be used to assess neuroticism. Outcome measure will be the number of physical symptoms, clinic visits, and disability days in each of these symptom areas assessed at three-month intervals for twelve months.